Hello Everyone, In this video, we will talk about How to Monitor
the Results of a nonlinear simulation as the model is solved. This can come in very handy
in identifying potential issues with the setup and resolve them before it finishes to solve,
especially when the model take a long time to run.
Let’s see how this is done!
Some nonlinear structural models can be time-consuming and challenging to solve.
Therefore, monitoring
their status and understanding how to diagnose potential issues such as rigid body motion
during the solution is critical in identifying issues as early as possible.
Doing this can save us a lot of time.
Rigid body motion may occur in an analysis
when contact goes undetected, or when the user defines any boundary conditions incorrectly.
When this happens, a simulation may either fail to converge or it may proceed to solve
a physical problem that is different from our model objective.
It’s important to note that there are two ways of monitoring nonlinear solutions –
- Monitoring the convergence behavior and tracking the converged results.
The former allows us to
check the convergence pattern, to see if the solution is progressing smoothly or not.
The latter gives us insight regarding the actual intermediate answers up to that point.
Several real-time solution response graphs such as force, displacement and other convergence
plots, solver output file and various other items help us monitor the status of convergence
which can be helpful in monitoring the convergence pattern of the solution.
Instead, we’ll focus our attention on reviewing intermediate results
through the use of result trackers.
This helps us view specific results such as stresses, strains, displacements
and contact results for substeps that have converged, so they are actual, valid solutions.
They help us in identifying potential issues with the model instead of having to wait after
the entire solution has completed.
In Ansys Mechanical, the result tracker feature
is available for the Structural, Thermal and Explicit analysis.
Depending on the type of
analysis, relevant result trackers are available for monitoring.
In this video we will demonstrate
this feature on a static Structural analysis.
While many results trackers are available
for structural analysis, in this video we will use Deformation result plot tracker and
Contact results tracker since they are commonly used for diagnostic purposes.
The deformation result plot tracker enables to plot the total deformation for the solution
available so far, so we can verify if the model is behaving as expected.
Contact results tracker is used for monitoring various contact outputs specific to a given
contact pair.
Using this one can monitor any changes in contact status, loss of contact,
or changes in other contact specific quantities such as stiffness, gaps, penetration, etc.
Let’s go ahead and show how result trackers can be used in a simple nonlinear example
to identify the problems in the model early in the solution process.
This model consists of a rigid indenter and a rigid base, and an elastomer sample
modeled using hyperelastic material model.
The objective of the simulation is to study
how the sample deforms due to indentation.
Due to the symmetry in the geometry and
the load, this model is suitable for a 2D axisymmetric analysis, but for demonstration
purpose we have decided to model it as a 3D model with cyclic symmetry on a 30-degree sector.
The Indenter and the base are modeled as
rigid bodies, assuming that we are not interested in the results for the rigid bodies.
Frictionless contacts are used between the base and the elastomer, and indenter and the elastomer.
Notice that contact side should always be on the flexible geometry, in this
case the contact side of the contact pairs is on the elastomer.
A translational joint is scoped on the upper indenter face, to allow indenter to move in
the X direction only.
A fixed joint scoped to the lower face of
the base is used to fix the motion of the base in all directions.
Let’s go ahead and define a joint load, right click on static structural and insert
a joint load, and scope it to the translational joint. Change its type to Joint displacement.
Set the displacement to 2.5 mm so the indenter moves in the X direction by 2.5 mm.
Under Solution Information, insert Total Deformation result tracker, and scope it to
all bodies.
Next, Insert Contact tracker, scope it to
the frictionless contact between indenter and elastomer. Set type to Number of Contacting
to monitor the number of elements that are contacting during the solution.
Since indenter is going to be pushed down into the elastomer, we are expecting the number of contacting
elements to increase during the solution.
Go ahead and solve the model as set up.
Notice that the result trackers can also be defined on the go so the users need not
interrupt a run if they forgot to define them beforehand.
Now, click on the Contact tracker to monitor Number Contacting during the solution
You can see that the number of contacting elements immediately dropped, indicating the
loss of contact and possible rigid body motion.
Right Click on the Total Deformation tacker
and hit update to see the Total Deformation of the elastomer so far
You can see that the elastomer is not constrained properly, and it flew away.
The use of Result Trackers allows us to see that there is a possible problem in the
model before the entire solution completes, which can save us time.
Let’s go ahead and add symmetry boundary condition
Right mouse click on the Model and Insert Symmetry.
- Scope Symmetry to the side face of the elastomer.
- Select User defined coordinate system.
- Set symmetry Normal to the X axis.
- Next, repeat the steps to insert new symmetry object.
- Scope the symmetry to the opposite side of the elastomer.
- Select Global Coordinate system
- Set symmetry normal to Z axis.
Now, let's solve this model again.
- Click on the Contact tracker to monitor Number Contacting during the solution
We can see that there are several elements in contact now indicating that the contact
is established and there may not be any rigid body motion.
We can update the deformation plot tracker to confirm this behavior.
However, around the time of 0.4 sec we notice that the number of contacting elements decrease
significantly.
Let’s update the Deformation tracker to
see what may be causing this.
We can see lots of penetration due to elements skipping over the fillet.
This is because we did not include the full face of the indenter in our initial contact definition.
We always expect in this model that number
of contacting elements should increase. So if we have an idea of what to expect, result
trackers can either reassure us that the solution is progressing smoothly or they may warn us
when something unexpected is happening.
So let’s Stop the solution and fix this.
Deformation tracker is especially useful to give the snapshot of what is occurring
right now.
Let’s adjust the model one more time
Under frictionless contact between indenter and elastomer, Add extra surface for the target.
Go ahead and Hit solve.
Click on the Contact tracker.
Although number contacting increases and then decreases a little, this amount is relatively
small and number contacting doesn’t decrease below the initial contact.
Click on the Deformation tracker.
Deformation shows expected behavior.
We don’t have to rely only on 1 tracker to monitor the progress of the solution
Now let’s change the contact tracker to monitor penetration.
In this case the penetration
seems reasonable but if we wish to reduce it further, we may increase the contact stiffness
and such a decision can be made on the go by using contact tracker.
Sometimes, the contact stiffness might be
too high and may cause element distortion errors, in that case we may reduce it for
better convergence behavior.
This way, one can use different result trackers
to monitor the progress of solution and identify any necessary remedial changes on the go.
This completes the demo, now let’s summarize this discussion.
In this video we showed you how to use results trackers to monitor the results during the
solution process.
These tools can help us to save a lot of time while solving complex
and computationally expensive models.
Using Result Trackers provide several advantages
such as: - They help us in identifying any incorrect
model setup without having to wait for the model to finish running.
This can save us time, especially while solving time taking models.
They help us in monitoring solution progressing without stopping the solution
Using contact trackers, one can identify any rigid body motion that may be caused due
to loss of contact.
This concludes the video; we hope that this
video was helpful. Give the result trackers a try the next time you’re solving any complex
nonlinear models in Ansys Mechanical to monitor the solution progress.
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